Convert DER to PEM — Free Online DER Certificate Converter
Convert a DER binary certificate (.der, .cer) to Base64 PEM format for use with Nginx, Apache, and OpenSSL — 100% in-browser.
Frequently Asked Questions
Understanding DER and PEM Certificate Encoding
X.509 certificates are defined using ASN.1 (Abstract Syntax Notation One), a platform-independent data structure format. When storing or transmitting this certificate, you have a choice of encoding: DER binary or PEM Base64 text.
DER (Distinguished Encoding Rules) is the raw binary serialization. A 2048-bit RSA certificate in DER is typically 900–1100 bytes of compact binary data. Java's keytool, Android's certificate stores, and many IoT/embedded TLS libraries prefer DER because it eliminates the parsing overhead of Base64 decoding.
PEM is the same DER data encoded in Base64 and wrapped with ASCII headers. A PEM file is human-readable in a text editor. It is roughly 33% larger than DER due to Base64 overhead, but it can be safely embedded in configuration files, email, and shell scripts. OpenSSL, Nginx, Apache, HAProxy, and virtually all Linux/Unix SSL tooling expects PEM.
This conversion is mathematically lossless — Base64-decode the PEM body and you get back the exact DER bytes you started with. The certificate information, validity period, public key, and signatures are completely unchanged.